Coating composition for subbing polystyrene film



United States Patent 3,010,838 COATING COMPOSITION FOR SUBBINGPOLYSTYRENE FILM Jay J. Uber, South Hadley, Mass., assignor to ThePlastic Coating Corporation No Drawing. Filed July 13, 1959, Ser. No.826,433 3 Claims. (Cl. 106-128) This invention relatesto a coatingcomposition for use in the production of a photographic film having apolystyrene base sheet.

Polystyrene film has heretofore been proposed for use as a photographicfilm support and is finding increasing commercial use for this purpose.A serious problem has heretofore been presented in securing a firm bondbetween the surface of a polystyrene base sheet and the lightsensitivecoating of a gelatin-silver halide emulsion. Various solutions have beenproposed for the solution of this problem. 1

One proposed solution has been the application of an intermediatesubbing layer consisting of two or more coatings of differentcompositions. This solution to the problem has the disadvantage ofrequiring two or more coating operations to form the subbing, prior tothe application of the light-sensitive coating, thereby increasing thecost of the product.

Another solution to the problem has involved the substitution of aspecial light-sensitive coating for the conventional gelatin-silverhalide emulsion. This solution to the problem has the dual disadvantageof requiring a material and complex deviation from the normal proceduresfor the application of the conventional gelatin-silver halide emulsioncoatings, with increased cost arising both from the more expensiveingredients used in the special light-sensitive coating composition andthe complex procedure involved in the formulation of the light-sensitivecoating composition. A third solution to this problem has involved acombination of the foregoing alternative solutions which combines theeconomic disadvantages of each of those alternatives.

Specific examples of each of these alternative solutions to this problemare described by US. 2,816,027, issued December 10, 1957, to Thomas H.Farrell et al. While describing in considerable detail these alternativesolutions to the problem, that patent states that for certain purposesit is not necessary to apply a subbing to polystyrene sheeting beforecoating it with a photographic emulsion, especially where thephotographic film is to be employed at comparatively high relativehumidity. However, as a practical matter the application of a subbingcoating to a polystyrene base sheet is essential in the production ofphotographic film intended for any normal usage.

It will be understood that the term subbing is used in thisspecification in its usually accepted sense to mean an intermediate filmor coating on the surface of a base sheet or film which bonds aphotographic gelatin-silver halide emulsion to the surface of the basesheet or film.

It is an object of this invention to provide a coating composition whichis adapted for application to a polystyrene sheet or film in a singlecoating operation to form a subbing which will receive and firmly bond aconventional light-sensitive gelatin-silver halide coating to thepolystyrene base sheet or film.

Other objects of this invention and its various advantageous featureswill become apparent from the detailed description which follows:

The coating composition in accordance with this invention comprisesgelatin, nitrocellulose, acetic acid and phenol, a cresol, i.e. meta-,paraor ortho-cresol or a mixture of cresols dispersedin a suitablevolatile solvent for nitrocellulose. It may contain about 0.5% to about2.0%, by weight, of gelatin and preferably contain an amount within therange of about 0.75%, to about 1.5%, by weight, thereof. It may containan amount of nitrocellulose within the range of about 0.25% to about2.25%, by weight, and preferably within the range of about 0.75%, byweight, to about 1.5% by weight. It will contain an amount of phenol, acresol or a mixture of cresols within the range of about 1.0% to about5.0%, by weight, and preferably 2.0% to about 4.0%, by weight. Theacetic acid content of the composition may be within the range of 1.5%to about 6.0%, by weight, and preferably will be within the range ofabout 2.0% to about 4.0%, by weight.

It is a well recognized fact that the strength of nitrocellulose varieswith its viscosity characteristic with the strength falling off rapidlywith the lower viscosity types. Despite this well-known fact, I havefound in the case of a subbing film deposited from the composition ofthis invention, that its bonding strength increases when the lowerviscosity types of nitrocellulose are used in the composition. Anitrocellulose having a viscosity characteristic of 15 seconds givesvery poor adhesion between a photographic gelatin-silver halide emulsionfilm and a polystyrene surface. It is desirable to use a nitrocellulosein this coating composition which has a viscosity characteristic withinthe range of about 10 centipoises to about 5 seconds, and I prefer touse a nitrocellulose having a viscosity characteristic of within therange of about 10 centipoises to about /2 second. A 15 centipoise nitrocellulose has been found to give excellent results in this composition.The viscosity characteristic of a nitrocellulose of a type higher than Asecond may be measured by the standard falling ball method described byASTM specification D30l-50, while viscosity characteristics of A secondor lower can be conveniently measured by the use of a capillaryviscometer described for example on page 30 of the HerculesNitrocellulose Handbook published by Hercules Powder Company. Thenitrocellulose may be of the RS type or the SS type.

The phenol, the cresol, or the mixture of cresols in this composition isbelieved to increase the adhesion of the composition to the surface ofthe polystyrene sheet or film. It remains more or less completely in thecoating film which remains after the evaporation of the volatilesolvents. The acetic acid in the composition acts as a solvent for thegelatin in the composition and permits its solution in the anhydroussolvent for the nitrocellulose.

The polystyrene which is subbed by the use of the composition of thisinvention to form the base sheet or film of a photographic film is ofthe flexible type which may be produced by methods known in the art, US.Patent 2,074,285, issued March 16, 1937, to E. Studt et al., discloses amethod for the production of such sheets. The polystyrene sheet or filmmay be of any desired thickness and will usually have a thickness withinthe range of about 0.002 inch to 0.020 inch.

The photographic silver halide emulsion which is supplied over thesubbing on the polystyrene is of the conventional type. Typicalphotographic silver halide emulsions include silver chloride, silverbromide, silver iodide, silver brorniodide, silver chlorobromide andsilver chlorobromiodide emulsions. The carrier for the silver halide isgelatin.

The coating composition in accordance with this invention isspecifically illustrated by the following example:

The composition illustrated by Example 1 may be applied to polystyrenefilm in an amount within the range of about 6.5 lbs. to about 16.5 lbs.(wet coating weight) .per 1000 square feet.

As will be understood from the foregoing, the amounts of gelatin, ofnitrocellulose, of glacial acetic acid and of phenol shown by Example 1may be varied. In general, the ratio of nitrocellulose to gelatin shouldbe within the range of about 0.5 to 1.5 parts by weight for each part byweight of'gelatin. A cresol or a mixture of 'cresols can be substitutedfor phenol on a weight for weight basis. Example 2 gives ranges ofproportions which may be used in the coating composition.

EXAMPLE 2 Ranges of proportions of ingredients for coating compositionfor subbing-polystyrene film Percent by wt.

Gelatin 0.50-1.50 Nitrocellulose (viscosity within the range ofcentipoises to /2 second) 0.25-2.25

Glacial acetic acid 1.50-6.00

Phenol or cresol 1.00-5.00

Volatile solventv mixture The remainder In the foregoing, variousdetails have been given to fully explain the nature of this invention.However, it will be fully understood that various changes andmodifications can be made in'those details without departing from thespirit of this invention or the scope of the claims which follow.

I claim:

1. A coating composition consisting essentially of about 0.5%, byweight, to about 2.0%, by weight, of gelatin; about 0.5%, by weight, toabout 2.25%, by weight, of nitrocellulose having a viscositycharacteristic no higher than 5 seconds as measured by the standardmethod ASTM specification: D30l-50; about 1.5% by weight about 6.0%, byweight, of acetic acid; about 1.0%, by weight, to about 5.0%, by weight,of a material selected from the group consisting of phenol, orthocresol, meta cresol, para cresol and mixtures of cresols; and a volatileorganic solvent for the said nitrocellulose.

2. A coating composition consisting essentially of about 0.5%, byweight, to about 2.0%, by weight, of gelatin; about 0.5%, by weight, toabout 2.25%, by Weight, of nitrocellulose having a viscositycharacteristic no higher than /2 second as measured by the standardmethod ASTM specification D301-; about 1.5% by weight about 6.0%, byweight, of acetic acid; about 1.0%, by weight, to about 5.0%, by weight,of a material selected from the group consisting of phenol, orthocresol, meta cresol, para cresol and mixtures of cresols; and a volatileorganic solvent for the said nitrocellulose.

3. A coating conposition consisting essentially of about 0.75%, byweight, to about 2.0%, by weight, of gelatin; about 0.75%, by Weight, toabout 1.5%, by weight, of nitrocellulose having a viscositycharacteristic of no higher than /2 second as measured by the standardmethod ASTM specification D30l-50; about 2.0%, by Weight, of aceticacid; about 2.0%, by weight, to about 4.0%, by weight, of a materialselected from the group consisting of phenol, ortho cresol, meta cresol,para cresol and mixtures of cresols; and a volatile solvent for the saidnitrocellulose.

Starch Feb. 3, 1959

1. A COATING COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 0.5%, BYWEIGHT, TO ABOUT 2.0%, BY WEIGHT, OF GELATIN, ABOUT 0.5%, BY WEIGHT, TOABOUT 2.25%, BY WEIGHT, OF NITROCELLULOSE HAVING A VISCOSITYCHARACTERISTIC NO HIGHER THAN 5 SECONDS AS MEASURED BY THE STANDARDMETHOD ASTM SPECIFICATION D301-50, ABOUT 1.5% BY WEIGHT ABOUT 6.0%, BYWEIGHT, OF ACETIC ACID, ABOUT 1.0%, BY WEIGHT, TO ABOUT 5.0%, BY WEIGHTOF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF PHENOL, ORTHOCRESOL, META CRESOL, PARA CRESOL AND MIXTURES OF CRESOLS, AND A VOLATILEORGANIC SOLVENT FOR THE SAID NITROCELLULOSE.